Chemical control of nodding thistle (Carduus nutans L.) in New Zealand pastures

Broadcast sprays of several herbicides were applied at different times of the year at several sites in Hawkes Bay, Canterbury and Otago. For good thistle control, date of application was more important than types of herbicide. In Hawkes Bay, applications made in April, May and June tended to be the most effective. Under slightly cooler Canterbury conditions, April, September and October were the best application dates. In the Otago trials, spring emergence of thistle seedlings meant that the most consistent results came from September or October applications. At all sites, applications made in July or August were relatively ineffective, probably because of low winter temperatures and slow thistle growth rates. MCPA (potassium salt) at 1·0 kg ha^?1 was the standard herbicide used in all experiments. MCPA at 0·5 kg ha^?1, MCPB (sodium salt) at 0·5 and 1·0 kg ha^?1 and 2,4-D at 0·5 kg ha^?1 did not kill as many thistles as MCPA at 1·0 kg ha^?1. MCPA at 1·5 kg ha^?1 and MCPB (butyl) ester + clopyralid at 0·5 + 0·015 or 1·0+0·03 kg ha^?1 gave consistently better control than MCPA at 1·0 kg ha^?1 2,4-D at 1·0 or 1·5 kg ha^?1, MCPB at 1·5 or 2·0 kg ha^?1, and MCPA + MCPB at 0·33 + 1·0 or 0·67 + 0·5 kg ha^?1 gave results very similar to MCPA at 1 kg ha^?1. Thistle control varied between sites and years. Some of the variation may have been due to different proportions of first and second year thistles present at spraying, and to variation in genetically determined herbicide susceptibility. Chemical control of thistles was short term only, because of dormant seeds in the soil.     

Host specificity studies on Ceuthorhynchidius horridus (Panzer) (Coleoptera: Curculionidae) for the biocontrol of musk and plumeless thistle

Host specificity studies on Ceuthorhynchidius horridus (Panzer), a weevil which attacks thistles at the rosette stage, revealed that the larvae of this insect were able to complete development in musk thistle (Carduus nutans L.), plumeless thistle (Carduus acanthoides L.) and bull thistle (Cirsium vulgare (Savi) Ten.); but not in two closely related economic species, artichoke (Cynara scolymus L.) and safflower (Carthamus tinctorius L). Adult weevils showed feeding preference for the three thistles over artichoke; there was no feeding on safflower. Weevils that fed on thistles readily oviposited in artichoke as well as in thistles, but not in safflower. Feeding on artichoke was minimal and artichoke-fed weevils produced a subnormal number of eggs. Few larvae feeding in artichoke survived to the third instar; larval growth rate was slow and none pupated. Safflower did not support larval development or adult feeding. Recherches sur la spécificite de l'hôte chez Ceuthorhynchidius horridus (Panzer) (Coleoptères: Curculionidae) en vue de la lutte biologique contre le chardon penché et le chardon à feuilles d'acanthe Des recherches sur la spécificité de l'hôte chez Ceuthorhynchidius horridus (Panzer), un charançon qui attaque les chardons au stade rosette, ont révélé que les larves de cet insecte étaient susceptibles d'un développement complet chez le chardon penché (Carduus nutans L.) le chardon à feuilles d'acanthe (Carduus acanthoides L.) et le chardon commun (Cirsium vulgare (Savi) Ten.), mais non sur deux espèces très voisines; l'artichaut (Cynara scolymus L.) et le carthame (Carthamus tinctorius L.). Les charançons adultes ont manifesté une préférence à se nourrir des trois espèces de chardons plutôt que de l'artichaut. Le charthame n'a pas été consommé. Les charançons nourris sur les chardons ont déposé facilement leurs Æufs sur l'artichaut aussi bien que sur les chardons, mais pas sur le carthame. La consommation sur artichaut a été minimale et les charançons élevés sur artichaut ont produit un nombre d'Æufs plus élevé. Quelques larves élevées sur artichaut ont survécu jusqu'au troisième stade larvaire. Le taux de croissance des larves a été lent et aucune n'a formé de pupes. Le carthame n'a pas permis le développement des larves ni Ia nourriture des adultes. Untersuchungen zur Wirtsspezifität von Ceuthorhynchidius horridus (Panzer) (Coleoptera: Curculionidae) zur biologischen Bekämpfung von Carduus nutans L. und C. acanthoides L. Untersuchungen zur Wirtsspezifität von Ceuthorhynchidius horridus (Panzer), einem Rüsselkäfer, der die Disteln im Rosettenstadium befällt, zeigten, dass sich die Larven dieses Insekts in Nickender Distel (Carduus nutans L.), Weg-Distel (Carduus acanthoides L.) und Gemeiner Kratzdistel (Cirsium vulgare (Savi) Ten.) vollsändig entwickeln können, nicht hingegen in den zwei nahe verwandten Arten Artischocke (Cynara scolymus L.) und Färber-Saflor (Carthamus tinctorius L.). Ausgewachsene Rüsselkäfer zogen zum Fressen die drei Distelarten der Artischocke vor, auf Saflor wurde kein Frass beobachtet. Rüsselkäfer, die auf den Disteln frassen, legten ihre Eier sowohl in Artischocken als auch in Disteln ab, jedoch nicht in Saflor. Der Frass an der Artischocke war gering und die Rüsselkäfer auf diesen Pflanzen legten weniger Eier als normal. In den Artischocken überlebten nur wenige Larven das dritte Stadium, wuchsen langsamer und verpuppten sich nicht. Saflor begünstigt nicht die Entwicklung der Larven oder den Frass der erwachsenen Tiere.     

Uptake, translocation, metabolism and selectivity of glyphosate in Canada thistle and leafy spurge

The uptake, translocation and metabolism of glyphosate [N-(phosphonomethyl) glycine] by Canada thistle (Cirsium arvense (L.) Scop.) (susceptible) and leafy spurge (Euphorbia esula (L.)) (resistant) were examined in an attempt to elucidate the nature of the differential sensitivity. The pattern of uptake and translocation was similar in both species. Glyphosate moved readily in the apoplast and the symplast. High humidity and/or surfactant greatly increased the amount of ¹⁴C-glyphosate absorbed and translocated over that in low humidity and/or without surfactant. No ¹⁴Cmetabolites were detected in either species 1 week after treatment with ¹⁴C-glyphosate. More of a glyphosate spray solution containing a fluorescent dye was received and retained on Canada thistle by virtue of its growth habit than on leafy spurge. More glyphosate should therefore be available for uptake by Canada thistle and this may account for the differential sensitivity of these two species.     

Glyphosate effects on Canada thistle (Cirsium arvense) roots, root buds, and shoots

Glyphosate ? ? Mention of irademark or proprietary product does not constitute a gtiarantee or warranty oC the product by the U.S. Department of Agriculture and does nut imply its approval to the exclusion of other products thai may also be suitable.
was sprayed at 0009–1·12 kg a.i. ha^?1 on the foliage of large potted glasshouse-grown Canada thistle [Cirsium arvense (L.) Scop.], which had extensive, well-developed roots. Increasing the glyphosate rate progressively reduced the total number of visible adventitious root buds plus emerged secondary shoots per plant proportionately more than root biomass, 10 days after treatment. Cortical tissue of thickened propagative roots became soft, water-soaked, darkened, and some regions decomposed, exposing strands of vascular tissue. Lateral roots completely decomposed. When thickened roots were segmented to stimulate secondary shoot emergence from root buds 10 days after foliar treatment, Fewer secondary shoots emerged than expected from the number of visible adventitious root buds present on both control and herbicide-treated plants. Increasing the rate of glyphosate also reduced the regrowth potential of root buds proportionately more than root biomass. Regrowth potential was measured as the number of emerged secondary shoots 35 days after segmenting unearthed roots from plants that had been sprayed 10 days earlier. When foliar-applied at 0·28 kg ha^?1, glyphosate decreased the regrowth potential of root buds to zero in 2 and 3 days, as measured by secondary shoot dry weight and number, respectively, even though root fresh weight was unchanged 3 days after foliar treatment. These dose-response and time-course experiments demonstrate that glyphosate did not reduce root biomass as much as it decreased root bud numbers and secondary shoot regrowth potential from root buds.     

The allelopathic activity of Californian thistle (Cirsium arvense (L.) Scop.) in Tasmania

The phytotoxicity of extracts from the roots and foliage of Cirsium arvense (L.) Scop, was studied using seven test species. Water and alcohol extracts of C. arvense inhibited the germination of its own and Trifolium subterraneum L. seed, and inhibited the growth of its own seedlings, three annual thistles, and Lolium perenne L., T. subterraneum and Hordeum distichon L. The results are related to phytosociological patterns observed in the field, and it is suggest that the presence of phytotoxins in the soil may make the establishment of some pasture and crop species difficult in areas infested with C. arvense. Activité allélopathique du chardon Cirsium arvense L. Scop, en Tasmanie La phytotoxicityé d'extraits obtenus à partir des racines et du feuillage de Cirsium arvense (L.) Scop, a étéétudiée en tulisant sept espèces servant de tests. Des extraits aqueux et alcooliques de C. arvense inhibèrent sa propre germination et celle des semences de Trifolium subterraneum L. Ils inhibèrent également la croissance de ses propres plantules, de trois chardons annuels, de Lolium perenne L. de T. subterraneum et de Hordeum distichon L. Les résultats sont rapprochés des évolutions phytosociologiques observées au champ, et il est suggéré que la présence de phytotoxines dans le sol puisse rendre difficile l'implantation de certaines espèces fourragères ou autres dans les endroits infestés par C. arvense. Die allelopathische Aktivität von Cirsium arvense (L.) Scop. in Tasmanien Wurzel- und Blattextrakte von Cirsium arvense (L.) Scop. wurden auf ihre phytotoxische Wirkung mit sieben Test-pflanzen geprüft. Wasser- und Alkoholauszüge von C. arvense hemmten die Keimung der eigcnen und der Samen von Trifolium subterraneum L. Das Wachstum der eigenen Keimlinge, sowie von drei annuellen Distelarten, von Lolium perenne L., T. subterraneum und von Hordeum distichon L, wurde gehemmt. Die Ergebnisse zeigen einen Zusammenhang mit pflanzensoziologischen Feldbeobachtungen und es ist denkbar, dass die Gegenwart von Phytotoxinen im Boden den Aufwuchs von Grünlandpflanzen und Feldfrüchten in Fiächen, die mit C. arcense verseucht sind, erschweren kann.     

Influence of pasture grass and legume swards on seedling emergence and growth of Carduus nutans L. and Cirsium vulgare L.

Swards of 10 pasture species (six grasses and four legumes) were established and planted with seeds of either of the thistle species Carduus nutans L. or Cirsium vulgare L., and emergence and growth of the thistle seedlings were subsequently monitored. Emergence of C. nutans seedlings was inhibited by ryegrass (Lolium perenne L.) and Yorkshire fog (Holcus lanatus L.) swards, while C, vulgare emergence was inhibited by Yorkshire fog relative to some of the other treatments. Speed of emergence of C. nutans and absolute emergence of C. vulgare seedlings were significantly negatively correlated with pasture cover density, presumably as a consequence of alteration of light quality by the pasture swards. All pasture species inhibited seedling shoot and root growth of both thistle species, although the grasses were the most effective inhibitors. The seedling emergence and growth data for C. nutans in the swards of the 10 species were significantly correlated with the results of a previous study on residual allelopathic effects of the same 10 species on nodding thistle root growth. It is concluded that inhibitory (including allelopathic) influences of pasture species on thistle seedlings have considerable potential as a mechanism for managing problematic thistle populations. Influence de converts de pature de graminees et de legumineuses sur la levée et la croissance de Carduus nutans L. et Cirsium vulgare L. Des couverts de 10 espèces fourrageres (6 graminées et 4 légumineuses) ont étéétablis et infestés avec des graines de 1'une ou 1'autre des espèces de chardon, Carduus nutans L. et Cirsium vulgare L.; la levée et la croissance des plantules de chardon ont été ensuite suivies. La levée des plantules de C. nutans a été inhibéee par les couverts de ray-grass (LoliumperenneL.) et de houlque laineuse (Holcus lanatus L.) tandis que la levée de C. vulgareétait inhibée par la houlque laineuse en comparaison de quelques-unes des autres modalites. La vitesse de levée de C. nutans et la levée globale de C. vulgare ont été corrélées négativement de façon significative avec la densité du couvert, probablement en conséquence de 1'altération de la qualité de la lumière par les tapis, fourragers. Toutes les espèces de fourrages ont inhibé la croissance des tiges et des racines des plantules des 2 espèces de chardon, bien que les graminèes aient été des inhibiteurs plus efficaces. La Ievée des plantules et les chiffres de la croissance de C. nutans dans les couverts des 10 espéces étaient correlées de façon significative avec les résultats d'une étude antérieure sur les effets allélopathiques résiduels de quelques-unes des 10 espèces sur la croissance racinaire du chardon. II est conclu que les effets inhibiteurs (y compris I'allélopathie) des espèces fourragères sur les plantules de chardon ont un potentiel considèrable pour gérer le problème des populations de chardon. Einfluβ von Weidegräser- und Leguminosen-Beständen auf Samenkeimung und Wachstum von Carduus nutans L. und Cirsium vulgare L. In Beständen von 10 Weide-Pflanzenarten (6 Gräser und 4 Leguminosen) wurden Samen der Disteln Carduus nutans L. und Cirsium vulgare L. ausgebracht und deren Keimung und Wachstum beobachtet. Die Keimung von Carduus nutans wurde in Beständen von Weidelgras (Lolium perenne L.) und Wolligem Honiggras (Holcus lanatus L.) gehemmt, während die Keimung von Cirsium vulgare in Wolligem Honiggras genauso wie in einigen anderen Beständen gehemmt war. Die Keimungsgeschwindigkeit von Carduus nutans und die gesamte Keimung von Cirsium vulgäre waren signifikant negativ mit der Dichte der Weide-Pflanzenbestände korreliert, vermutlich wegen Änderung der Lichtqualität durch die Pflanzendecke. Alle Weide-Pflanzenarten, besonders jedoch die Gräser, hemmten das Sproß- und Wurzelwachstum der Keimpflanzen der beiden Disteln. Keimung und Wachstum der Carduus-nutans-Keimpflanzen in den Beständen der 10 Arten entsprachen ganz den Befunden einer früheren Untersuchung über allelopathische Wirkungen derselben 10 Arten auf das Wurzelwachstum der Nickenden Distel. Den Hemmwirkungen (einschließlich allelopathischen) von Weide-Pflanzenarten auf Distel-Keim-pflanzen kommt offenbar eine erhebliche Bedeutung für die Unterdrückung problematischer Distelpopulationen zu.     

Absorption and translocation of 14C-3,6-dichloropicolinic acid in Cirsium arvense (L.) Scop.

Experiments were conducted in a growth cabinet to investigate the absorption and translocation of ¹⁴C-3, 6-dichloropicolinic acid by Cirsium arvense (L.) Scop. (Canada thistle, creeping thistle), a sensitive species. Applications were made, either to the middle four leaves of 12-cm-tall vegetative plants grown under low (40%) and/or high (>95%) relative humidity (r.h.), or to four upper or lower leaves of 30-cm-tall flowering plants grown under low r.h. Following application to vegetative plants, absorption and translocation of ¹⁴C-3,6-dichloropicolinic acid was rapid and was approximately doubled by high r.h. High r.h. increased the amount of radioactivity retained by the treated leaves or translocated to the shoots but did not affect greatly the amount retained in the roots. The herbicide was highly mobile, with over half of that absorbed, translocated out of the treated leaves after two days. The apex accumulated most of the radioactivity, while approximately 8% was recovered from the roots. The absorption and translocation patterns were similar to those reported in the literature for picloram in C. arvense. Absorption of 3,6-dichloropicolinic acid was greater in vegetative than in flowering C. arvense plants, and placement of herbicide on lower leaves tended to decrease the amount of radioactivity recovered from shoot apex and increase the amount recovered from the roots. Approximately 15% of the applied radioactivity could not be recovered from treated plants by 2 days after treatment.     

Bentazone selectivity between soybean and Canada thistle*

Postemergence applications of bentazone [3-iscpropyl-1H-2,1,3-benzothiadiazine-4-(3H)-one-2,2-dioxide] have shown promise for weed control in soybean [Glycine max (L.) Merr.]. A high soil moisture regime reduced soybean tolerance to bentazone. Covering the soil with vermiculite prior to spraying avoided the loss in tolerance and suggested that bentazone absorption by roots can occur under conditions of flooding at time of application. Bentazone was more inhibitory to photosynthesis 3 h after application and to respiration 1 day after application to the susceptible Canada thistle [Cirsium arvense (L.) Scop.] than to the tolerant soybean. The retention of less spray on leaf surfaces and faster metabolism of absorbed bentazone by soybean appear lo contribute to the observed selectivity. Movement of the ¹⁴C-label from the site of ¹⁴C-bentazone application in either species was primarily acropetal within the treated leaf. Sélectivité de la hentazone vis-á-vis du soja et du chardon Des applications en postlevée de bentazone (3-isopropyl-1H-2,1,3-benzothiadiazine-4-(3H)-one,2,2-dioxyde) se sont nion-trées prometteuses pour de désherbage du soja (Glyeine max (L.) Merr.). Un taux élevé d'humidité du sol a réduit la résistance du soja á la bentazone. Le recouvrement du sol avec de la vermiculite avant le traitement a évité la perte de resistance, de qui suggere que rabsorption de la bentazone par les racines peut se produire lorsqu'il y a submersion au moment du traitement. La bentazone s'est montré e plus inhibitrice pour la phclosynthé se 3 heures apré s l'application, et pour la respiration, 1 jour apré s Tapplication, pour le chardon, (Cirsium arvense (L.) Scop.) plante sensible, que pour le soja, plante risistante. La retention plus faible du liquide pulvérisé sur les surfaces foliaires et le métabolisme plus rapide de la bentazone par le soja semble contribuer á la sélectivité observé e. La migration du ¹⁴C depuis le site d'application de la ¹⁴C-bentazone dans les deux espéces a ite au début acropétale á l'intérieur des feuilles traitées. Selektivität von Bentazon zwisehen Sojabohne und Acker-Kratzdistel Die Verwendung von Bentazon [3-Isopropyl-1H-2,1,3-benzothiadiazin-4-(3H)-one-2,2-dioxid] im Nachauflaufver-fahren zur Unkrautbekämpfung in Sojabohnen [Glyeine max. (L.) Merr.] ist vielversprechend. Hohe Bodenfeuch-tigkeit verminderte die Toleranz von Bentazon gegenüber der Sojabohne. Bedecken des Bodens mit Vermikulit vor der Spritzung bewirkte, dass die Kultur nicht geschSdigt wurde und lässt daher vermuten, dass Bentazon über die Wurzeln aufgenommen wird. wenn zur Zeit der Anwendung der Boden sehr feucht ist. Bentazon hemmte 3 h nach der Applikation die Photosynthese und einen Tag nach der Anwendung die Atmung bei der Acker-Kratzdistel (Cirsium arvense (L.) Scop.] stärker als bei der toleranten Sojabohne. Die geringere Rentention auf der Biattobertiäche und der raschere Metabo-lismus des aufgenommenen Bentazons scheint zur Selektivitat bei der Sojabohne beizutragen. Aktivität von ¹⁴C-Bentazon wurde im Blatt beider Arten hauptsachlich akropetal transloziert.     

Characteristics of seeds and seedlings from weeds treated with sublethal herbicide doses

Size, germination and viability of seeds as well as growth of seedlings derived from three weed species were studied in a pot trial. Fallopin convolvulus (L.) A. Loeve, Galium. spurium L. and Thlaspi arvense L. were treated with MCPA or tribenuron-methyl at four doses and at five growth stages, from seedling stage to flowering, In G. spurium subnormal doses of tribenuron-methyl, applied at intermediate growth stages, greatly reduced seed weight, gennination, viability, seedling shoot biomass and root biomass. Germination and viability, as well as the shoot biomass and root biomass of seedlings, were highly correlated with seed weight. In addition, but to a smaller extent, seed weight was reduced in F. convolvidus and T. arvense by tribenuron-methyl and in G. spurium by MCPA. Germination was reduced in F. convolvulus by MCPA and in T. arvense by tribenuron-methyl. However, the effects varied greatly depending on the growth stage at application.     

Effect of sodium 2,2,3,3-tetrafluoropropionate on the germination, emergence, growth and survival of pasture species

The effect of sodium 2,2,3,3-tetrafluoropropionate (tetrapion) on the germination, emergence, growth and survival of pasture species was ascertained in petri-dishes (21 days) and in soil (114 days). Tetrapion was applied with the water in the petri-dishes and to the soil surface prior to sowing seeds 2-mm deep in plastic-lined glasshouse trays. The rates applied in the petri-dishes were 0,0.093, 0.187, 0.375, 0.75 and 1.5 kg a.i. ha^?1; the same rates, except 0.093 kg a.i. ha^?1, were applied in the glasshouse. In the petri-dishes tetrapion did not affect germination rate nor germination capacity of any species. However, it severely reduced shoot growth (22–78% for the lowest and highest rate, respectively) and moderately reduced root growth per seedling (4–44% for lowest and highest rate). In the glasshouse trays, lower emergence, at 27 days, of five of the sown species on the 1.5 kg a.i. ha^?1 treatment compared with the control, was explained by depression of shoot growth. Emergence was not affected at any other rate. Between day 27 and day 114 there was a progressive decline in the number of living seedlings of all species; the magnitude of deaths increased with time and rate of tetrapion. The rating of species for tolerance to tetrapion was: Medicago sativa > Festuca arundinacea > Dactylis glomerata > Phalaris aquatica > Eragrostis curvula. Although Trifolium subterraneum seedlings survived low rates of tetrapion they were still affected at day 114 whereas seedlings of other species were recovering. As tetrapion is readily leached from the soil profile, desirable species must be sown after sufficient rain has fallen to wash it from the soil. In this way it is possible to kill weed seedlings that germinate soon after spraying as well as to establish improved species.     

Growth of seedling Achillea millefolium L. (yarrow) in association with pea (Pisum sativum L.)

When Achillea millefolium L. (yarrow) seedlings were grown in the field in association with a pea (Pisum sativum L.) crop vegetative growth of yarrow was significantly reduced by 6 weeks after emergence. Flowering was totally suppressed while the pure stand of yarrow developed flower clusters at 13 weeks after seedling emergence. Rhizome development occurred at 8 weeks after seedling emergence in the pure stand, but not until 15 weeks when grown with pea. The early suppression of seedling yarrow in a glasshouse experiment was associated with root interference, although by 5 weeks shoot interference by pea plants was important in reducing yarrow growth. The greatest suppression of yarrow occurred when both roots and shoots of the two species were allowed to interfere. Yarrow had low aggressivity against pea when grown in various combinations in a replacement series experiment in the glasshouse.     

Influence of plant age on the allelopathic potential of nodding thistle (Carduus nutans L.) against pasture grasses and legumes

The allelopathic influence of four developmental stages of nodding thistle (small rosette, large rosette, bolting and dead plants) on eleven test species (six grasses, four legumes and itself) was investigated using aqueous extract bioassays, aqueous leachate bioassays, and bioassays based on addition of ground material to soil. The aqueous extract and leachate bioassays indicated that nodding thistle was most allelopathic at the rosette stages, while the bioassays involving amendment of soil with thistle tissue showed bolting live and dead plants to be the most allelopathic. It is proposed that nodding thistle is allelopathic at two phases of its development, i.e. at the early bolting stage when the larger rosette leaves are decomposing and releasing soluble inhibitors, and at the stage when bolting plants are dying and releasing insoluble inhibitors. Nodding thistle seedlings appear to be stimulated by addition of thistle tissues to soil, indicating that thistle plants may weaken pasture and simultaneously encourage recruitment of its own species. This is consistent with previous studies detecting high densities of thistle seedlings in the vicinity of deceased parent plants. The six grass species were generally more tolerant to thistle allelopathic effects than were the four legume species, but no consistent differences emerged between different grass or legume species. Influence de l'age de la plante sur le potentiel allélopathique du chardon penche (Carduus nutans L.) vis a vis des prairies de graminées et de légumineuses L'influence allélopathique de 4 stades de développement du chardon penché (petite rosette, grande rosette, montaison, plantes mortes) sur 11 espèces tests (6 graminées, 4 légumineuses et lui-même) a étéétudiée en utilisant des bioessais d'extraction acqueuse, des bioessais de lessivage acqueux et des bioessais fondés sur l'addition au sol d'amendement. Les bioessais d'extraction acqueuse et de lessivage ont montré que le chardon penchéétait plus allélopathique au stade rosette tandis que les bioessais impliquant l'amendement de sol avec des tissues de chardon ont montré que la montaison et les plantes mortes étaient les plus allélopathiques. Il est proposé que le chardon penché est allélopathique à 2 phases de son développement, par exemple au stade montaison précoce quand les plus grandes feuilles de la rosette se décomposent et relachent les inhibiteurs solubles, et au stade où les plantes montées meurent et relächent les inhibiteurs insolubles. Les plantules de chardon penché apparaissent être stimulées par l'addition de tissus de chardon au sol, montrant que les plantes de chardon peuvent affaiblir une prairie et simultanément favoriser sa propre réimplantation. Ceci est conforme avec des études précédentes montrant des fortes densités de plantules de chardon au voisinage de plantes parentes mortes. Les 6 espèces de graminées ont été de façon générale plus tolérantes aux effets allélopathiques que les 4 espèces de légumineuses, mais aucune différence importante ne s'est exprimée entre les différentes espèces de graminées ou de légumineuses. Einfluβ des Pflanzenalters der Nickenden Distel (Carduus nutans L.) auf die allelopathische Wirkung gegen Weidegräser und Leguminosen Die allelopathische Wirkung der Nickenden Distel wurde in 4 Entwicklungsstadien (in kleiner und in voller Rosette, blütentreibend und abgestorben) gegen 11 Pflanzenarten (6 Gräser, 5 Leguminosen und sich selbst) mit wäßrigen Auszügen, Perkolationswasser und Bodenmaterial zum Substrat geprüft. Mit den wäßrigen Auszügen und dem Perkolationswasser zeigte sich die Nickende Distel im Rosetten-Stadium am meisten allelopathisch, während Bodenmaterial mit Resten blütentreibender und abgestorbener Pflanzen wirksamer war. Es kann angenommen werden, daß die Nickende Distel in 2 Entwicklung sphasen allelopathisch wirkt, nämlich wenn die größeren Rosettenblätter oder wenn die blütentreibenden Pflanzen vergeben und 1ösliche Hemmstoffe entlassen. Keimpflanzen der Nickenden Distel werden offensichtlich durch Pflanzenmaterial der Distel im Wachstum angeregt; die Distel schwächt also Weide-Pflanzenarten und fördert zugleich ihre eigene Entwicklung. Dieser Befund deckt sich mit der Beobachtung hoher Keimpflanzen-Dichten um abgestorbenen Mutterpflanzen. Die 6 Gräser waren durchweg gegenüber der allelopathischen Wirkung der Distel unempfindlicher als die 4 Leguminosen, doch innerhalb dieser Gruppen zeigten sich keine klaren Unterschiede.     

Growth characteristics of spring barley and selected weeds. II. Effect of temperature and irradiance in growth chambers

As a part of a broader study, two experiments were carried out in growth chambers with three day/night temperature regimes (10/7, 20/14 and 30/21^C) studying growth characteristics of individual seedlings over a four-week period. Experiment 1 was performed with spring barley (Hordeum vulgare L.), Galeopsis tetrahit L., and Viola Arvensis Murray. Experiment 2, with three irradiance levels at 20/14^C, and one irradiance level at the other temperatures, was performed with spring barley, V. arvensis, Chenopodium album L., Brassica rapa L. sspoleifera (DC.) Metzger, and Stellaria media (L.) Vill. Leaf area, dry weight, relative growth rate, net assimilation rate, and net photosynthetic rate generally showed an optimum at 20/14^C. Increasing irradiance resulted in a decreased specific leaf area. Expressed as fraction of shoot dry weight, green leaves decreased and stems, flowers, and yellow leaves increased with increased time, irradiance, and temperature. At all temperatures, barley, B. rapa and G. tetrahit had the largest dry weights, but at 20/14^C. C album and S. media and at 30/21^C C. album also had large values. Differences in dry weight between species correlated more to morphological features than to assimilation rate.     

Potential allelopathic effects of Mikania micrantha on the seed germination and seedling growth of Coix lacryma‐jobi

The allelopathic potential of Mikania micrantha H.B.K. to affect the seed germination and seedling growth of Coix lacryma‐jobi L. was investigated. Water‐soluble allelopathic substances were found in the water extracts of M. micrantha. The effect of the water extracts on the seed germination and seedling growth of C. lacryma‐jobi was concentration‐dependent. The water extracts from the different plant parts (leaf, stem, and root) of M. micrantha differed in their effect on the germination and seedling growth of C. lacryma‐jobi, with the effect of the leaf extract being the least inhibitory. The malondialdehyde (MDA) content in the C. lacryma‐jobi seedlings increased by 64%, 45%, and 52% of the control with increasing concentrations of the extracts of the root, stem, and leaf (80, 400, and 400 g L^?1, respectively). The extract from the M. micrantha roots significantly increased the catalase (CAT) activity of the C. lacryma‐jobi seedlings (48% and 54% of the control at the concentrations of 20 g L^?1 and 80 g L^?1, respectively). The extracts from the leaves and stems at low concentrations increased the CAT activity, but at high concentrations, the extracts decreased the CAT activity. The extracts from the roots, stems, and leaves at concentrations of 80, 400, and 400 g L^?1 also significantly decreased the peroxidase (POD) activity of the C. lacryma‐jobi seedlings to 27%, 52%, and 34% of the control, respectively. These results indicate that the water extracts of M. micrantha could inhibit the seed germination and seedling growth of C. lacryma‐jobi through the regulation of anti‐oxidase activity, such as POD and CAT in the cells. The growth inhibition of the C. lacryma‐jobi seedlings is probably related to injury after oxidization of the cell membranes with the increase of MDA content.     

Determination of Festuca filiformis seedbank characteristics,seedling emergence and herbicide susceptibility to aid management in lowbush blueberry (Vaccinium angustifolium)

Festuca filiformis is a common perennial grass in lowbush blueberry fields, but little is known about the general biology, seedbank characteristics, seedling recruitment or susceptibility of seedlings to currently registered herbicides. The objectives of this research were to determine (i) the presence of F. filiformis seedbanks in lowbush blueberry fields, (ii) whether F. filiformis seedbanks accumulate near the soil surface in lowbush blueberry fields, (iii) the dormancy status of fresh F. filiformis seeds, (iv) the temporal patterns of seedling recruitment in established F. filiformis populations, (v) whether F. filiformis has a vernalisation requirement for flowering in lowbush blueberry and (vi) susceptibility of F. filiformis seedlings to various herbicides currently registered in lowbush blueberry. Festuca filiformis formed a seedbank in lowbush blueberry fields, with an average of 1660 ± 272–5680 ± 1409 seedlings m^?2 emerging from soil cores collected from two infested fields. Most seeds were located at the soil surface, providing opportunities for seedbank management through predation or burning. Fresh seeds lacked dormancy and readily germinated, although germination was reduced by dark conditions. New seedlings emerged in spring and autumn and required vernalisation to flower. Seedlings were susceptible to several currently registered herbicides in lowbush blueberry, although mortality rates were highest in plants treated with glufosinate, flumioxazin, glufosinate + flumioxazin and terbacil. Growers should avoid movement of seeds on machinery, and additional research should be conducted to determine the effects of registered herbicides on F. filiformis seedling recruitment under field conditions in lowbush blueberry.     

The allelopathic effect of three Amaranthus spp. (pigweeds) on wheat (Triticum durum)

The allelopathic effect of Amaranthus retroflexus L., Amaranthus blitoides S. Wats, and Amaranthus gracilis Desf. on wheat Triticum durum L. was investigated under laboratory, glasshouse and field conditions. Laboratory experiments showed that fresh shoot or root extract of the three weed species reduced germination, coleoptile length, root length and root dry weight of wheat seedlings. The inhibitory effects were rate dependent, with low concentrations of shoot extract promoting shoot growth of wheat. Fresh plant extracts were more phytotoxic than dried plant extracts and shoot extracts had higher detrimental effects than root extracts. In pot experiments, dried shoot extract of A. gracilis increased shoot and root dry weights of wheat seedlings. For A retroflexus and A. blitoides the extracts of these and dried shoots (8 g kg^?1), which had been added to soil mixtures significantly reduced ger-mination and growth of wheat seedlings. Addition of up to 16 g kg^?1 of A. gracilis residues promoted shoot growth of wheat and had no significant harmful effect on root growth. Roots appeared more sensitive to allelopathic effect than shoots. Under field conditions, incorporation of A. retroflexus or A. blitoides residues in the soil reduced height, grain and straw yield of wheat, whereas A. gracilis residues stimulated plant height and increased yield.     

Mesotrione control and pigment concentration of large crabgrass (Digitaria sanguinalis) under varying environmental conditions

BACKGROUND: Mesotrione is a carotenoid biosynthesis‐inhibiting herbicide currently labeled for crabgrass (Digitaria spp.) control. Mesotrione control of large crabgrass has been reported to vary with temperature and relative humidity; however, the effect of irradiance on mesotrione efficacy has not previously been reported. Likewise, little is known about pigment concentrations of Digitaria spp. The present research investigated the effects of mesotrione on large crabgrass, Digitaria sanguinalis (L.) Scop., control and pigment concentrations under varying irradiance at three temperatures. RESULTS: Mesotrione (0.28 kg ha^?1) control of large crabgrass did not differ between temperature levels (18, 26 and 32 °C). Control was similar at tested irradiance levels (600, 1100 and 1600 µmol m^?2 s^?1). Mesotrione reduced large crabgrass chlorophyll a, chlorophyll b and total carotenoid concentrations, as well as chlorophyll a to b ratios. Treated plant bleaching was highest 7 days after treatment (DAT) but decreased by 21 DAT. Treated plants were less than 10% necrotic 3 and 7 DAT but nearly 35% necrotic 21 DAT. Treated large crabgrass bleaching was highest and photochemical efficiency was lowest 7 DAT. These results indicate that some plant recovery occurs prior to 21 DAT. CONCLUSION: Although mesotrione efficacy has previously been reported to vary according to environmental factors, mesotrione control of large crabgrass did not vary with measured temperature and irradiance levels in this study. On account of crabgrass convalescence, secondary applications of mesotrione may control large crabgrass more effectively when applied prior to 21 DAT. Copyright © 2009 Society of Chemical Industry     

Uprooted buffelgrass thatch reduces buffelgrass seedling establishment

Buffelgrass (Pennisetum ciliare (L.) Link), a non-native perennial bunchgrass, invades ecologically intact areas of the Sonoran Desert. It competitively excludes native plants and increases fire frequency and intensity. Since the 1990s, whole buffelgrass plants have been manually uprooted and removed to control the invasion in southern Arizona. Uprooting plants results in bare, disturbed soil which promotes buffelgrass seed germination. This study examined whether leaving entire uprooted buffelgrass plants (thatch) on a field site reduces future buffelgrass establishment compared to removing uprooted plants from the site. A secondary goal was to determine whether light reduction and autoallelopathy were major factors in the negative effect of thatch on buffelgrass seedling density. Field plots with an average of 8,095 kg/ha thatch had 1.9 buffelgrass seedlings/m² which was significantly fewer than the 2.9 seedlings/m² in plots without thatch. Thatched portions of thatch plots (50% of their total area) had only 0.7 seedlings/m². In the greenhouse, which reduced outdoor light intensity by 35.2%, buffelgrass seeds sown in bare soil resulted in significantly higher seedling density than beneath buffelgrass thatch. Potential autoallelopathic chemicals leached from partially decomposed buffelgrass thatch and leached thatch had an intermediate but not significant (p = 0.09) effect on seedling numbers. Results suggest that leaving uprooted buffelgrass plants has the benefit of reducing seedling establishment in the area disturbed by uprooting.     

Growth of Elymus repens (L.) Gould and Agrostis gigantea Roth. at different light intensities

Elymus repens (L.) Gould and Agrostis gigantea Roth. raised from rhizomes both responded to reduced light intensity by increased stem length, while the number of aerial shoots was reduced. The weight of the aerial parts was not influenced by a 50% reduction of the daylight intensity, but a further reduction of light caused a significant decrease in weight. The production of new rhizomes was more influenced by shading than were the aerial shoots. The consequence was an increase in the shoot/rhizome ratio. The food reserve per bud measured as inter-node weight in E. repens and A. gigantea was reduced only with intensive shading, and the vitality of the rhizomes appeared independent of light intensity. Intensive shading in early as compared to late summer caused a reduction in the number and weight of aerial shoots, but not in the weight of new rhizomes. Light intensities equal to those found in a spring wheat crop allowed more E. repens growth than light intensities equal to those in a spring oat crop. E. repens raised from seeds and grown at light intensities equal to those found in a cereal crop, showed insignificant rhizome production.     

A study of competition between seedlings of gorse (Ulex europaeus L.) and perennial ryegrass (Lolium perenne L.) by means of a replacement series experiment

Competiton between seedlings of gorse (Ulex europaeus L.) and perennial ryegrass (Lolium perenne L cv. Grasslands Nui) was studied in a replacement series experiment under glasshouse conditions. Without cutting, the shoot growth of gorse in monoculture exceeded that of ryegrass over 22 weeks but was reduced more by competition from ryegrass than the grass growth was reduced by competition from gorse. The root system of gorse was small compared with that of ryegrass and was further reduced by competition. Cutting three times at 2 or 4 cm reduced the total growth of both species and gorse was affected more than ryegrass. With grass, however, the ‘growth between succeeding cuts declined faster than that of gorse and in the final harvest period, gorse in monoculture oulyielded ryegrass. The relative crowding coefficients of gorse were low compared with those of ryegrass and their products consistently exceeded 1.0. The results are discussed in relation to lirmiting seedling establishment of gorse in the field.